Slide A
Pulmonary embolism: This large thromboembolus is lodged at the bifurcation of the pulmonary artery ("saddle embolus"). Its size and shape suggests its origin in a leg vein.

Slide B
Pulmonary embolus and infarct: A thromboembolus is lodged in a peripheral branch of a pulmonary artery (arrow). Note the hemorrhagic area of lung distal to this, representing flooding of alveoli by blood derived from the bronchial circulation via collateral flow.